1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Description of the Related Art
Many technologies have been developed for treating automotive exhaust gasses. However, since the amount of traffic has been increased, reducing the automotive exhaust gasses has not been sufficiently performed. The automotive exhaust gas emission control will be further tightened in Japan and the world. In the automotive exhaust gas emission control, NOx control in diesel vehicle exhaust gasses has been severely tightened. Conventionally, the amount of NOx has been reduced by controlling an engine combustion system; however, only controlling the engine combustion system has not been sufficient. In order to meet the control, as a diesel vehicle NOx treating system, a NOx reduction system called an SCR system which uses ammonia as a reducing agent has been proposed.
As a catalyst carrier which is used in the system, a honeycomb structure is known. In WO2005/063653, a honeycomb structure formed of honeycomb units is disclosed. In forming the honeycomb unit, a material is prepared by mixing γ alumina, ceria, zirconia, zeolite, and the like with inorganic fibers and an inorganic binder, the mixed material is molded into a honeycomb shape, and the honeycomb-shaped molded body is fired; with this, the honeycomb unit is formed.
In Japanese Patent 2675321, a NOx treating method is disclosed in which NOx in diesel engine exhaust gases is reduced by using ammonia. In the method, a honeycomb catalyst is used in which an equivalent diameter of a through hole of a cell is 1.5 to 5 mm, the thickness of cell walls is 0.3 to 0.9 mm, and a pore volume in a specific pore range of the total pore volume is 40% or more.
The entire contents of WO2005/063653 and Japanese Patent 2675321 are hereby incorporated by reference.